1. Field of the Invention
The present invention relates to imaging technology for diagnosis based on 3-dimensional (3D) medical images, and particularly relates to a 3-dimensional diagnostic imaging system for use in locating an affected part and making a differential diagnosis using a 3-dimensional ultrasound image and another type of 3-dimensional diagnostic modality image in a complementary manner.
2. Description of the Related Art
Cancer is one of three major diseases in Japan today. Of the three major diseases, cancer is the only disease with an increasing mortality. Accordingly, there are strong social demands for improved treatment as well as diagnosis of cancer. In particular, liver cancer represents about 10% of all cancer diseases and unfortunately, the mortality from liver cancer is increasing.
As for diagnosis of liver cancer, early detection has been made possible by recent technological advances in medical diagnostic imaging modalities, such as an ultrasound diagnostic imaging apparatus, an MRI scanner, and an X-ray CT scanner.
An X-ray CT scanner realizes a 3-dimensional imaging technique by combining a multiraw (8-raw, 16-raw, 64-raw, or the like) detector with a high-speed helical scanner. With an MRI scanner, 3-dimensional imaging can be performed in a short time with one breath-holding. This is made possible by advances in high-speed imaging techniques associated with improved performance of a gradient magnetic field system, a high-frequency magnetic field system, an RF coil system, and the like. Thus, with advances in 3-dimensional imaging techniques, very high diagnostic ability compared to that achieved by conventional 2-dimensional imaging techniques has been achieved. Particularly significant advances in 3-dimensional diagnostic imaging have been made in 3-dimensional dynamic CT (hereinafter referred to as 3-dimensional CT) with a contrast agent.
As for treatment for liver cancer, the following four types are known: (a) transcatheter arterial embolization, (b) transcatheter arterial chemo-embolization, (c) minimally invasive treatment, and (d) abdominal surgery. Of the four types, minimally invasive treatment is most widely used, as it is less invasive to the patient.
Examples of this minimally invasive treatment include a percutaneous ethanol injection technique (PEIT) and microwave ablation. A minimally invasive treatment is performed with a puncture needle, which is monitored through its real-time image acquired by an ultrasound diagnostic imaging apparatus.
Of various ablation treatments, radio-frequency ablation (RFA) is in the limelight and its clinical application is in progress. Examples of RFA include cool-tip RFA performed with a single needle and RITA performed with a plurality of needles. These ablation treatments are currently under clinical evaluation. In many cases, puncture is performed percutaneously. In some cases, treatment is laparoscopically performed using the same puncture device as described above while observing the surface of the liver or while observing the inside of the liver through its surface using an ultrasound transducer.
However, despite the recent technological advances in 3-dimensional diagnostic imaging and therapeutic/diagnostic puncture, 3-dimensional medical diagnostic images are not effectively used in planning or treatment of puncture or in aftercare. Ultrasound images used in clinical practice are local diagnostic images which do not allow simultaneous observation of the entire liver and adjacent parts, such as a diaphragm and the like. Thus, there is a need for techniques that make it possible to easily find a proper needle insertion point on a 3-dimensional CT image.
Moreover, since therapeutic puncture is performed by means of ultrasound imaging, there is a need to display, on a 3-dimensional image, an easy-to-understand 3-dimensional CT cross-sectional image (virtual ultrasound image) representing a possible image of an ultrasound cross section including a puncture needle to be observed during puncture treatment. There is also a need to display a determined needle insertion point relative to a body surface and bones.
In recent years, there have been proposed various techniques for displaying a virtual ultrasound cross-sectional image superimposed on a 3-dimensional CT image, for example, in JP-A 2002-112998, JP-A 2005-169070, or US 2005/0033160 A1. Thus, real-time virtual ultrasound imaging systems have been commercially available.
JP-A 2002-112998 proposes a puncture assisting apparatus for displaying, on the basis of 3-dimensional volume data, a cross section image according to the position and angle of an ultrasound transducer used in puncture. However, with this assisting apparatus, it is difficult to determine whether there is an obstacle on or near the path along which to insert a puncture needle.
In a technique for displaying a virtual ultrasound cross-sectional image superimposed on a 3-dimensional CT image, there is a problem in that a part to be treated can be seen only on an X-ray CT image and cannot be seen or cannot be easily seen on an ultrasound diagnostic image. Another problem is that if there are two or more parts to be treated, it is difficult to perform effective treatment on the basis only of images obtained in planning of treatment.
Also, in a technique for displaying a virtual ultrasound cross-sectional image superimposed on a 3-dimensional CT image, due to characteristics of ultrasound puncture treatment, an ultrasound image displayed on an ultrasound diagnostic imaging apparatus is a 2-dimensional cross-sectional image. Such a 2-dimensional cross-sectional image is limited to a CT cross-sectional image or the like that is substantially identical to a cross-sectional image acquired at a position which allows acquisition of an image with an ultrasound transducer. Therefore, it is difficult to make comparison, after treatment, among images acquired by different modalities.